Renesas R-Car Gen3 Digital Radio Interface controller (DRIF)
------------------------------------------------------------

R-Car Gen3 DRIF is a SPI like receive only slave device. A general
representation of DRIF interfacing with a master device is shown below.

+---------------------+                +---------------------+
|                     |-----SCK------->|CLK                  |
|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
|                     |-----SD0------->|D0                   |
|                     |-----SD1------->|D1                   |
+---------------------+                +---------------------+

As per datasheet, each DRIF channel (drifn) is made up of two internal
channels (drifn0 & drifn1). These two internal channels share the common
CLK & SYNC. Each internal channel has its own dedicated resources like
irq, dma channels, address space & clock. This internal split is not
visible to the external master device.

The device tree model represents each internal channel as a separate node.
The internal channels sharing the CLK & SYNC are tied together by their
phandles using a property called "renesas,bonding". For the rest of
the documentation, unless explicitly stated, the word channel implies an
internal channel.

When both internal channels are enabled they need to be managed together
as one (i.e.) they cannot operate alone as independent devices. Out of the
two, one of them needs to act as a primary device that accepts common
properties of both the internal channels. This channel is identified by a
property called "renesas,primary-bond".

To summarize,
   - When both the internal channels that are bonded together are enabled,
     the zeroth channel is selected as primary-bond. This channels accepts
     properties common to all the members of the bond.
   - When only one of the bonded channels need to be enabled, the property
     "renesas,bonding" or "renesas,primary-bond" will have no effect. That
     enabled channel can act alone as any other independent device.

Required properties of an internal channel:
-------------------------------------------
- compatible:	"renesas,r8a7795-drif" if DRIF controller is a part of R8A7795 SoC.
		"renesas,rcar-gen3-drif" for a generic R-Car Gen3 compatible device.

		When compatible with the generic version, nodes must list the
		SoC-specific version corresponding to the platform first
		followed by the generic version.

- reg: offset and length of that channel.
- interrupts: associated with that channel.
- clocks: phandle and clock specifier of that channel.
- clock-names: clock input name string: "fck".
- dmas: phandles to the DMA channels.
- dma-names: names of the DMA channel: "rx".
- renesas,bonding: phandle to the other channel.

Optional properties of an internal channel:
-------------------------------------------
- power-domains: phandle to the respective power domain.

Required properties of an internal channel when:
	- It is the only enabled channel of the bond (or)
	- If it acts as primary among enabled bonds
--------------------------------------------------------
- pinctrl-0: pin control group to be used for this channel.
- pinctrl-names: must be "default".
- renesas,primary-bond: empty property indicating the channel acts as primary
			among the bonded channels.
- port: child port node corresponding to the data input, in accordance with
	the video interface bindings defined in
	Documentation/devicetree/bindings/media/video-interfaces.txt. The port
	node must contain at least one endpoint.

Optional endpoint property:
---------------------------
- sync-active: Indicates sync signal polarity, 0/1 for low/high respectively.
	       This property maps to SYNCAC bit in the hardware manual. The
	       default is 1 (active high).

Example:
--------

(1) Both internal channels enabled:
-----------------------------------

When interfacing with a third party tuner device with two data pins as shown
below.

+---------------------+                +---------------------+
|                     |-----SCK------->|CLK                  |
|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
|                     |-----SD0------->|D0                   |
|                     |-----SD1------->|D1                   |
+---------------------+                +---------------------+

	drif00: rif@e6f40000 {
		compatible = "renesas,r8a7795-drif",
			     "renesas,rcar-gen3-drif";
		reg = <0 0xe6f40000 0 0x64>;
		interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&cpg CPG_MOD 515>;
		clock-names = "fck";
		dmas = <&dmac1 0x20>, <&dmac2 0x20>;
		dma-names = "rx", "rx";
		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
		renesas,bonding = <&drif01>;
		renesas,primary-bond;
		pinctrl-0 = <&drif0_pins>;
		pinctrl-names = "default";
		port {
			drif0_ep: endpoint {
			     remote-endpoint = <&tuner_ep>;
			};
		};
	};

	drif01: rif@e6f50000 {
		compatible = "renesas,r8a7795-drif",
			     "renesas,rcar-gen3-drif";
		reg = <0 0xe6f50000 0 0x64>;
		interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&cpg CPG_MOD 514>;
		clock-names = "fck";
		dmas = <&dmac1 0x22>, <&dmac2 0x22>;
		dma-names = "rx", "rx";
		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
		renesas,bonding = <&drif00>;
	};


(2) Internal channel 1 alone is enabled:
----------------------------------------

When interfacing with a third party tuner device with one data pin as shown
below.

+---------------------+                +---------------------+
|                     |-----SCK------->|CLK                  |
|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
|                     |                |D0 (unused)          |
|                     |-----SD-------->|D1                   |
+---------------------+                +---------------------+

	drif00: rif@e6f40000 {
		compatible = "renesas,r8a7795-drif",
			     "renesas,rcar-gen3-drif";
		reg = <0 0xe6f40000 0 0x64>;
		interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&cpg CPG_MOD 515>;
		clock-names = "fck";
		dmas = <&dmac1 0x20>, <&dmac2 0x20>;
		dma-names = "rx", "rx";
		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
		renesas,bonding = <&drif01>;
	};

	drif01: rif@e6f50000 {
		compatible = "renesas,r8a7795-drif",
			     "renesas,rcar-gen3-drif";
		reg = <0 0xe6f50000 0 0x64>;
		interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&cpg CPG_MOD 514>;
		clock-names = "fck";
		dmas = <&dmac1 0x22>, <&dmac2 0x22>;
		dma-names = "rx", "rx";
		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
		renesas,bonding = <&drif00>;
		pinctrl-0 = <&drif0_pins>;
		pinctrl-names = "default";
		port {
			drif0_ep: endpoint {
			     remote-endpoint = <&tuner_ep>;
			     sync-active = <0>;
			};
		};
	};
